code: def _construct_symbolic_bu(q, sigma, m):
      return (
          (m - 1) / 2 * sp.erfc(sp.erfcinv(2 * q / (m - 1)) - 1 / sigma)
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import math
  from absl import app
  import numpy
  import scipy
  import sympy
  import core
label_desc: Use image node_id 18 for calling a global function with example usage: _construct_symbolic_bu(q, sigma, m) and returns: unknown